Welcome to CS 100

1. Welcome to CS 100 • Goal: Learn to write intelligible, correct computer programs • Language: Java (but the language should not be the primary focus) • Software: CodeWarrior • Plan: Compressed, intense version of a full-semester course. Be sure to keep up! Lecture 1

2. Course Staff • Instructor: Lynette Millett, millett@cs • TAs: • Wei Tsang Ooi, weitsang@cs.cornell.edu • Alan Renaud, ajr5@cornell.edu • David Welte, dcw6@cornell.edu • Consultants: • Rocky Chen, pjc4@cornell.edu, Young Ho Cho, yc102@cornell.edu, Amanda Waack, amw18@cornell.edu Lecture 1

3. Logistics • Lectures every day (Mon-Fri) • Roughly two assignments per week • NO LATE ASSIGNMENTS ACCEPTED • 0 or more short quizzes per week • Partners: 1 partner allowed where specified • Highest level of academic integrity expected Lecture 1

4. Logistics continued • Office hours: as noted on web • One prelim: Monday, July 19, 1999 • Final Grades: • 50% assignments • 25% prelim • 25% final • First Assignment due this THURSDAY Lecture 1

5. When Turning in Assignments: • No late assignments accepted • Your name and Cornell ID# should be on frontpage (in comments, if a program) • For programming assignments turn in printout of source code, sample output and disk • For written assignments: please type. TAs reserve right not to grade illegible homework. Lecture 1

6. Main Concepts Today • What is an algorithm? • Method and method call • Reading this week: Chapter 1 (skim), Chapters 2 and 3 • Handouts Lecture 1

7. Algorithm • A set of instructions for performing some task that is: • precise • unambiguous • effective • abstract • In other words: well-specified Lecture 1

8. Examples of Algorithms • A recipe for chocolate mousse • Given this list of integers, tell me which ones are even • Play a game of tic-tac-toe in a way that you never lose • Find your Star Wars name Lecture 1

9. Star Wars example: Lynette Millett born in Norway, ME to I. (Rogers) Millett becomes: Mil+Ly = Milly Ro+Nor = Ronor • First SW name: Write first 3 letters of your last name then attach first 2 letters of your first name • Last SW name: Write first 2 letters of mother’s maiden name and attact first 3 letters of hometown Lecture 1

10. Ambiguous Algorithm • Take two pieces of bread • Put peanut butter on one side of one piece • Put jelly on one side of the other piece • Put the pieces together • Output of this algorithm is. . . . Lecture 1

11. A Messy Sandwich • Why? • The algorithm did not specify that the pieces of bread should be put together so that the peanut butter and jelly are on the inside • Computers do exactly what they’re told or, worse, something undefined • Precision is important • Any other ambiguities in that example? Lecture 1

12. Programs • A program is an algorithm written in some language: English, C++, Java, . . • “Computer program” is a program in a computer language such as Java • Abstraction vs. Representation • Algorithm -- Program • Number -- Numeral • Object having “threeness” -- 3, III, three, ||| Lecture 1

13. How does it work? • Algorithm given as sequence of instructions to execute in order • In Java, each instruction is called a statement • Common statement in Java is a method call or method invocation • But, what’s a method? • “Method”, “procedure”, “function” often used interchangeably Lecture 1

14. Sample Method Heading // Draw a line from point (x1, y1) to point //(x2, y2) public void drawLine (int x1, int y1, int x2, int y2) • Comment: explains the method precisely in English. Always begin with “//” • Prefix modifiers public, void (will explain later) • Method name: drawLine • Parameters: x1, y1, x2, y2, and their types: int Lecture 1

15. Method Call // Draw a line from point (x1, y1) to point //(x2, y2) public void drawLine (int x1, int y1, int x2, int y2) • Call: drawLine(3, 5, 1, 1); • Command to be executed: Draw a line from point (3,5) to point (1,1) Lecture 1

16. Another Example // Print the largest of x, y and z public void printMax (int x, int y, int z) • Call: printMax(7, 83, 20*5-52); • Command to be executed: print the largest of 7, 83 and 20*5-52 • Note: the method name “printMax” has no meaning to Java. It is just a string of characters. We could have called it aaa, pm, mymethod, etc. . . Lecture 1

17. Yet Another Example // In the output window, skip a line and print // “Hello!” public void printHello() • Call: printHello(); • Command to be executed: In the output window, skip a line and print “Hello!” Lecture 1

18. Points to Remember • A method can have zero parameters • Syntax of a method call is: name(list of 0 or more arguments separated by commas); Lecture 1

19. What does the Method do? • To find out what a method does: • Make a copy of the specification (the comment in the heading) • replace all parameters by the appropriate arguments in the call • This assumes the programmer wrote good comments Lecture 1

20. Understanding Methods • The way we have understood these methods relies on comments that are • precise • understandable • correct • Your programs will be judged partially on how well your documentation is Lecture 1

21. Reading • From now on, consult syllabus and/or webpage. We will try to point out appropriate readings from the text, but you should use the text as a reference when solving homework problems. • URL: http://www.cs.cornell.edu/cs100-su99 Lecture 1

22. Assignment W1 • Series of questions requiring written answers • Should be fairly straightforward if you’ve done the reading • Due Thursday July 1 at the beginning of class Lecture 1

23. Registration Form • Please fill out and turn in before you leave class today. Lecture 1